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Subject:
From:
Rick Bell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Rick Bell <[log in to unmask]>
Date:
Wed, 18 Mar 2009 15:50:26 -0500
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Amol,

I have some admittedly limited experience with underfilling CSP's for increased reliability.  Some answers to your questions:

1.) Our material selection initially was governed by a host of parameters-- reworkability (see next point), minimum dispense gap, process temperatures, cte matching, filler content, etc.  In my experience, trying to get a reworkable version will greatly limit your choices.  

2.) We used a Loctite material, I believe it was 3549.  Please be aware that the term "reworkable" is relative.  We tried using it on polyimide flex substrates, and found its reworkability was a matter of interpretation.  Your mileage may vary...

3.) We used an Asymtek dispense jet platform with very good results as far as material deposition.  Our only inspection capability was outsourced CSAM.

4.) Pitfalls-- Our biggest issues were some minor problems with adhesion to the substrate/device, and incomplete encapsulation of a given solder joint due to poor capillary fill on our device (this has highly detrimental effects in temp cycle).  My only advice there is that if you're going to attempt a full encapsulation, have CSAM inspection available to verify your coverage, or some very tight process controls once you have a benchmarked process.

In the end, we elected to just do a corner bond approach, rather than trying to fully encapsulate the BGA array, and we had reasonable success in reliability improvement.







-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
Sent: Wednesday, March 18, 2009 2:48 PM
To: [log in to unmask]
Subject: [TN] Underfill Application

Dear Technetters,
We are about the develop a process for underfilling BGAs for a high reliability application. the underfill will be a rework able underfill. I wanted to poll the technet on:
1.      Guidance on material selection
2.      most common materials being used out there and the process equipment being used to do so.
3.      Common pitfalls and things to lookout for
4.      inspection techniques used to inspect the finished product
5.      a good source for info on underfilling (books, papers etc.,)

Thanks in advance.

Regards,
Amol





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